Many printing systems, such as those employed by various laser printers (and copy machines, multi-function printers and the like), utilize a printing process that is known as electrophotographic printing or, more simply, EP printing. Systems that are employed in EP processes are often fairly complex and designed within tight tolerances, all of which combines for a somewhat expensive product.
As an example, consider the following. In many laser printers, a laser source produces a laser that is projected towards a rapidly rotating polygonal mirror assembly having multiple facets. The mirror reflects the laser onto a rotating optical photoconducting drum or “OPC” whose surface is selectively charged or discharged in accordance with locations that are illuminated by the laser. This, in turn, allows toner to be selectively applied to the OPC in accordance with the print job that was received, which toner can then be applied to a print medium and suitably fused thereon.
As the printer receives data that is to be printed on the print medium, the data is processed into raster data that is used to modulate the laser. Raster data can be thought of as a series of 1s and 0s that are used to either turn the laser on or off. Raster data is typically used to serially modulate the laser as the mirror assembly rotates. That is, each facet of the mirror assembly typically corresponds to one line on the page. As the mirror assembly rotates through one facet, the raster data serially modulates the laser to produce one scan line on the OPC. As the next facet advances into the path of the laser, the raster data again serially modulates the laser to produce another adjacent scan line, and so on.
The desired rates of forming images on media can result in scanning assemblies that operate at high rotational rates. In addition, precise control of the scanning mirror rotational rate helps to achieve precise control of the position of discharged areas on scan lines. Furthermore, complex lenses are used to focus the laser on the surface of the photoconductor as the laser is swept across the scan line. Design constraints such as these contribute to the expense associated with scanning assemblies.